1. Field of the Invention
Methods and systems consistent with the present invention relate to registration of mobile nodes in a mobile Internet Protocol (IP) environment, and more particularly, to minimizing a time required for registering a mobile node by omitting an agent discovery procedure to be typically performed whenever a mobile node moves to a new subnet.
2. Description of the Related Art
Due to technological advancements in a mobile communication, mobile networks have changed from conventional channel-based mobile networks to packet-based mobile networks for a fast data processing. Most of the recent mobile communication services such as GPRS, CDMA2000-1X, 1X-EVDO, or W-CDMA adopt packet-based networks to process data. The demand for packet-based network is also increasing.
In such packet-based networks, a mobile IP address is given to each mobile node in order to allow the mobile nodes to have mobility without having to change their IP addresses. By obtaining the mobile IP address, each mobile node can remain in communication without having to reestablish upper-layer protocols, such as Transmission Control Protocol (TCP) while it is on the move.
However, in order to remain in communication with a correspondent node without interruption when the mobile node having the mobile IP address moves to a new subnet, the mobile node should obtain a new care-of-address (CoA) from a foreign agent (FA), i.e., a mobile IP agent of the new subnet, and register the CoA obtained from the FA to an original home agent (HA) in its home network.
For that reason, when the mobile node moves to a new subnet, the mobile node receives an agent advertisement message from a new FA, or voluntarily broadcasts an agent solicitation message to solicit the new FA to broadcast the agent advertisement message.
As a result, the mobile node is informed of its CoA through the agent advertisement message, and the CoA is registered again on the HA via the FA.
FIG. 1 is a network diagram for describing how a conventional system operates when a mobile node having a mobile IP address moves to a new foreign subnet.
For example, a mobile node 110 having its mobile IP address should go through an Agent Discovery procedure, a Registration procedure, and a Tunneling procedure in order to continuously transmit data to and receive data from a correspondent node 120 after the mobile node 110 moves from a home network 130 to a foreign network 140, and registers its location on an HA 135 in its home network 130 via an FA 145 of the foreign network 140.
During the Agent Discovery procedure, the mobile node 110 identifies the presence of the FA 145 in the new subnet (the foreign network) 140. This procedure may be performed through two methods. One method is that the FA 145 periodically broadcasts an agent advertisement message containing a CoA to the entire new subnet (the foreign network) 140 to which the FA 145 belongs, in order to announce its presence. The other method is that the mobile node 110 voluntarily broadcasts an agent solicitation message to the new subnet (the foreign network) 140 to solicit the new FA 145 to broadcast the agent advertisement message.
During the Registration procedure, the mobile node 110 registers its CoA obtained from the FA 145 during the Agent Discovery procedure on the HA 135 via the FA 145 through a registration request message. In other words, when the mobile node 110 broadcasts the registration request message containing its mobile IP address, CoA, and HA address, the FA 145 forwards the CoA to the HA 135. As a result, the HA 135 can identify the mobile node's location.
During the Tunneling procedure, a packet transmitted from the correspondent node 120 is forwarded to the HA 135, and the HA 135 transmits the received packet to the FA 145 through an IP tunneling. Then, the FA 145 forwards the received packet to the mobile node 110. In this case, a triangle routing problem occurs that the packet is transmitted from the correspondent node 120 to the mobile node 110 via the HA 135, thus unnecessarily causing the packet to go through the HA 135.
In order to solve such a problem, the correspondent node 120 transmits a binding request message, and a direct connection between the correspondent node 120 and the mobile node 110 is made through the binding update message.
A conventional method of minimizing packet losses during a handover operation is shown in FIG. 2. According to this method, a new FA transmits a binding update message to a previous FA, so that the packets buffered in the previous FA during the handover are not discarded but transmitted directly to the new FA.
On the other hand, a mobile node cannot obtain a new CoA until an agent advertisement message is received from the FA of the new subnet. As a result, the mobile node cannot register its location on an HA on its own.
Therefore, in the conventional system, if the agent advertisement message is not received from the new FA as well as from the previous FA, the mobile node broadcasts the agent solicitation message to the new subnet to solicit the new FA to broadcast the agent advertisement message. However, in a real-time communication, the time required for the Agent Discovery procedure may cause communication delay, degradation of quality of service, and even disconnection between the mobile node and the correspondent node.
Korean Unexamined Publication No. 2004-0073843 discloses a fast handover method in a mobile IP network environment. In this method, an access router transmits directly a response message through a routine cache table without notifying an upper-layer router, in case of a pre-registration message cached in the terminal. However, Korean Unexamined Publication No. 2004-0073843 does not disclose a method of solving the aforementioned problem occurring in the Agent Discovery procedure.
Accordingly, there a need for a method of registering the location of the mobile node on the HA, with quality of service being guaranteed without performing the Agent Discovery procedure.